DE 19632311 A1 discloses a control strategy for the actuation of a pump based on a pressure volume model, wherein the pump actuation is performed under the aspect of giving priority to the evacuation of the low-pressure accumulators. In this arrangement, the delivery rate of the hydraulic pump is dimensioned such that the time period between two successive phases of brake pressure reduction is sufficient for the complete evacuation of the low-pressure accumulators.
The prior-art pump actuation impairs the pedal comfort because the delivery volume flow is not in balance with the volume flow required (pressure increase pulses). Especially in situations where there is no risk of filling the low-pressure accumulators or when the pilot pressure exceeds the locking pressure level only slightly, a conventional pump actuation of this type is uncomfortable or even impairs the control quality (e.g. on a low coefficient of friction) because the pilot pressure is significantly modified due to an unbalanced return delivery. This change of the pilot pressure causes the known vibrating of the brake pedal during ABS intervention. The vibrating is the result of the brake pedal displacing in the direction of the vehicle bottom when pressure is built up because volume is consumed in a control operation. Hence, the brake pedal is moved in an opposite direction, towards the driver's foot, superimposed by the delivery pump's activity.